1. Field of the Invention
The present invention relates to an airbag apparatus that includes an airbag inflatable in a suitable inflation mode under control of a control device.
2. Description of Related Art
JP11-321506A discloses an airbag apparatus wherein the contour of the airbag at full inflation is controllable by a control device. This airbag apparatus includes a dual output inflator and an airbag that includes a bag body, an inner bag disposed inside the bag body and a tether that connects the bag body and inner bag while determining a clearance between the inner bag and bag body. The tether is sewn to part of the circumferential wall of the inner bag so as to reduce the volume of the airbag. The inflator includes a first operating section that feeds inflation gas into the bag body and a second operating section that provides inflation gas into the inner bag, and the inflator is configured operable in low-output mode where only the first operating section is actuated and in high-output mode where both the first and second operating sections are actuated, under control of the control device. In low-output mode, the first operating section operates to discharge inflation gas into the bag body only such that the airbag inflates in small-volume mode. In high-output mode the second operating section operates as well to feed inflation gas into the inner bag, and sewing threads that sew together the tether and the circumferential wall of the inner bag rupture due to the pressure of inflation gas flown into the inner bag, such that the tether is lengthened to allow the airbag to inflate in big-volume mode.
However, with the above configuration, there is a possibility that the sewing threads that sew the tether and circumferential wall of the inner bag fail to rupture thoroughly in big-volume mode and the airbag cannot secure a predetermined volume. Moreover, the timing of rupture of the sewing threads is hardly steady. Therefore, there is a room for improvement in inflating the airbag quickly and with a steady contour in big-volume mode.